Packaged micromirror assembly with in-package mirror position feedback

ABSTRACT

A packaged micromirror assembly ( 21, 21 ′) is disclosed. The assembly ( 21, 21 ′) includes a mirror element ( 41 ) having a mirror surface ( 29 ) that can rotate in two axes. Magnets ( 53 ) are attached to the mirror element ( 41 ), to permit rotation of the mirror surface ( 29 ) responsive to the energizing of coil drivers ( 36 ). A sensor ( 63, 80 ) is disposed under the mirror surface ( 29 ) to detect mirror orientation. In one aspect of the invention, the sensor ( 63 ) includes a light source such as an LED ( 68 ) that imparts light through an aperture ( 66 ) at the underside of the mirror surface ( 29 ). Light detectors ( 65 ) are arranged at varying angles, and detect relative intensity of light reflected from the underside of the mirror surface ( 29 ), from which the rotational position of the mirror ( 29 ) can be derived. According to another aspect of the invention, a conical sensor ( 80 ) with multiple insulated segmented capacitor plates are arranged under the mirror surface ( 29 ). Variations in the capacitance between the mirror ( 29 ) and the various segments of the sensor ( 80 ) indicate the position of the mirror ( 29 ). A calibration memory ( 77 ) may be provided, to store calibration values so that the sensor ( 63, 80 ) can be nulled with the mirror ( 29 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority under 35 U.S.C. §119(e)(1) ofprovisional application serial No. 60/233,851, filed Sep. 20, 2000.

[0002] This application is related to U.S. patent application entitledStacked Micromirror Structures, docket no. TI-31436, filed on Sep. 18,2001 and U.S. patent application entitled Molded Packages for OpticalWireless Network Micromirror Assemblies, docket no. TI-31437, filed onSep. 18, 2001.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0003] Not applicable.

BACKGROUND OF THE INVENTION

[0004] This invention is in the field of optical communications, and ismore specifically directed to micromirror assemblies as used in suchcommunications.

[0005] Modern data communications technologies have greatly expanded theability to communicate large amounts of data over many types ofcommunications facilities. This explosion in communications capabilitynot only permits the communications of large databases, but has alsoenabled the digital communications of audio and video content. This highbandwidth communication is now carried out over a variety of facilities,including telephone lines (fiber optic as well as twisted-pair), coaxialcable such as supported by cable television service providers, dedicatednetwork cabling within an office or home location, satellite links, andwireless telephony.

[0006] Each of these conventional communications facilities involvescertain limitations in their deployment. In the case of communicationsover the telephone network, high-speed data transmission, such as thatprovided by digital subscriber line (DSL) services, must be carried outat a specific frequency range to not interfere with voice traffic, andis currently limited in the distance that such high-frequencycommunications can travel. Of course, communications over “wired”networks, including the telephone network, cable network, or dedicatednetwork, requires the running of the physical wires among the locationsto be served. This physical installation and maintenance is costly, aswell as limiting to the user of the communications network.

[0007] Wireless communication facilities of course overcome thelimitation of physical wires and cabling, and provide great flexibilityto the user. Conventional wireless technologies involve their ownlimitations, however. For example, in the case of wireless telephony,the frequencies at which communications may be carried out are regulatedand controlled; furthermore, current wireless telephone communication oflarge data blocks, such as video, is prohibitively expensive,considering the per-unit-time charges for wireless services.Additionally, wireless telephone communications are subject tointerference among the various users within the nearby area. Radiofrequency data communication must also be carried out within specifiedfrequencies, and is also vulnerable to interference from othertransmissions. Satellite transmission is also currently expensive,particularly for bi-directional communications (i.e., beyond the passivereception of television programming).

[0008] A relatively new technology that has been proposed for datacommunications is the optical wireless network. According to thisapproach, data is transmitted by way of modulation of a light beam, inmuch the same manner as in the case of fiber optic telephonecommunications. A photoreceiver receives the modulated light, anddemodulates the signal to retrieve the data. As opposed to fiberoptic-based optical communications, however, this approach does not usea physical wire for transmission of the light signal. In the case ofdirected optical communications, a line-of-sight relationship betweenthe transmitter and the receiver permits a modulated light beam, such asthat produced by a laser, to travel without the waveguide of the fiberoptic.

[0009] It is contemplated that the optical wireless network according tothis approach will provide numerous important advantages. First, highfrequency light can provide high bandwidth, for example ranging from onthe order of 100 Mbps to several Gbps, using conventional technology.This high bandwidth need not be shared among users, when carried outover line-of-sight optical communications between transmitters andreceivers. Without the other users on the link, of course, the bandwidthis not limited by interference from other users, as in the case ofwireless telephony. Modulation can also be quite simple, as comparedwith multiple-user communications that require time or code multiplexingof multiple communications. Bi-directional communication can also bereadily carried out according to this technology. Finally, opticalfrequencies are not currently regulated, and as such no licensing isrequired for the deployment of extra-premises networks.

[0010] These attributes of optical wireless networks make thistechnology attractive both for local networks within a building, andalso for external networks. Indeed, it is contemplated that opticalwireless communications may be useful in data communication within aroom, such as for communicating video signals from a computer to adisplay device, such as a video projector.

[0011] It will be apparent to those skilled in the art having referenceto this specification that the ability to correctly aim the transmittedlight beam to the receiver is of importance in this technology.Particularly for laser-generated collimated beams, which can have quitesmall spot sizes, the reliability and signal-to-noise ratio of thetransmitted signal are degraded if the aim of the transmitting beamstrays from the optimum point at the receiver. Especially consideringthat many contemplated applications of this technology are in connectionwith equipment that will not be precisely located, or that may move overtime, the need exists to precisely aim and controllably adjust the aimof the light beam.

[0012] Copending application Ser. No. 09/310,284, filed May 12, 1999,entitled “Optical Switching Apparatus”, commonly assigned herewith andincorporated herein by this reference, discloses a micromirror assemblyfor directing a light beam in an optical switching apparatus. Asdisclosed in this application, the micromirror reflects the light beamin a manner that may be precisely controlled by electrical signals. Asdisclosed in this patent application, the micromirror assembly includesa silicon mirror capable of rotating in two axes. One or more smallmagnets are attached to the micromirror itself; a set of four coildrivers are arranged in quadrants, and are current-controlled to attractor repel the micromirror magnets as desired, to tilt the micromirror inthe desired direction.

[0013] Because the directed light beam, or laser beam, has an extremelysmall spot size, precise positioning of the mirror to aim the beam atthe desired receiver is essential in establishing communication. Thisprecision positioning is contemplated to be accomplished by way ofcalibration and feedback, so that the mirror is able to sense itsposition and make corrections.

BRIEF SUMMARY OF THE INVENTION

[0014] It is an object of the present invention to provide a package fora micromirror assembly that includes sensing capability for the positionof the micromirror.

[0015] It is a further object of the present invention to provide amethod for making such a package.

[0016] It is a further object of the present invention to provide such apackage and method that is relatively low-cost, and also well suited forhigh-volume production.

[0017] Other objects and advantages of the present invention will beapparent to those of ordinary skill in the art having reference to thefollowing specification together with its drawings.

[0018] The present invention may be implemented into a package for amicromirror assembly. The package is molded around a plurality of coildrivers, and their control wiring, for example by injection or transfermolding. A two-axis micromirror and magnet assembly is attached to ashelf overlying the coil drivers. Underlying the mirror is a sensor forsensing the angular position of the mirror. According to the preferredembodiment of the invention, the sensor includes a light-emitting diodeand angularly spaced light sensors that can sense the intensity of lightemitted by the diode and reflecting from the backside of the mirror. Theposition of the mirror can be derived from a comparison of theintensities sensed by the various angularly positioned light sensors.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0019]FIG. 1a is a schematic drawing of an optical wireless networkusing a packaged micromirror assembly.

[0020]FIG. 1b is a schematic drawing of an optical wireless networkusing a packaged micromirror assembly according to the preferredembodiments of the invention.

[0021]FIGS. 2a and 2 b are plan and cross-sectional views, respectively,of a packaged micromirror assembly according to a first preferredembodiment of the invention.

[0022]FIG. 3 is a plan view of a mirror element in the packagedmicromirror assembly according to the first preferred embodiment of theinvention.

[0023]FIGS. 3a through 3 d are cross-sectional views of the mirrorelement of FIG. 3, illustrating its operation.

[0024]FIGS. 4a and 4 b are plan and cross-sectional views, respectively,of a packaged micromirror assembly according to a first preferredembodiment of the invention.

[0025]FIGS. 5a through 5 c are various views of a packaged micromirrorassembly according to a second preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be described in connection with itspreferred embodiments, with an example of an application of thesepreferred embodiments in a communications network. It is contemplated,however, that the present invention may be realized not only in themanner described below, but also by way of various alternatives whichwill be apparent to those skilled in the art having reference to thisspecification. It is further contemplated that the present invention maybe advantageously implemented and used in connection with a variety ofapplications besides those described below. It is therefore to beunderstood that the following description is presented by way of exampleonly, and that this description is not to be construed to limit the truescope of the present invention as hereinafter claimed.

[0027] Referring first to FIG. 1a, an example of an optical wirelessnetwork will be illustrated, to provide context for the presentinvention. In this simple example, unidirectional communications are tobe carried out from computer 2 to server 20, by way of modulateddirected light. In this example, computer 2 is a conventionalmicroprocessor based personal computer or workstation, including theappropriate network interface adapter for outputting the data to becommunicated. Computer 2 is connected to transmitter optical module 5,which aims a directed light beam at the desired receiver 17, and whichmodulates the light beam to communicate the data.

[0028] Alternatively, the transmitting source may be a network switch orrouter, a source of video data such as a DVD player or a televisionset-top converter box, or the like, rather than computer 2 as shown. Itis contemplated that the present invention may be used in connectionwith effectively any source of digital data.

[0029] In this example, transmitter optical module 5 includes modulatinglaser 6, which generates a collimated coherent light beam of the desiredwavelength (e.g., 850 nm) and power (e.g., on the order of 4 to 5 μW/cm²measured at 50 meters, with a spot size of on the order of 2.0 to 2.5 mmin diameter). Modulating laser 6 modulates this light beam according tothe digital data being transmitted. The modulation scheme usedpreferably follows a conventional data communications standard, such asthose used in connection with fiber optic communications for similarnetworks. The modulated laser beam exits modulating laser 6 and isreflected from micromirror assembly 10 toward receiver 17. Theconstruction of micromirror assembly 10 according to the preferredembodiments of the invention will be described in further detail below.

[0030] On the receiver end, receiver 17 captures the incoming directedlight beam, and converts the modulated light energy to an electricalsignal; for example, receiver 17 may include a photodiode, whichmodulates an electrical signal in response to the intensity of detectedlight. Such other conventional receiver circuitry, such as demodulators,filters, and the line, are also provided. The demodulated communicatedelectrical signal is then forwarded from receiver 17 to router 18, andthus into the receiving network, for eventual distribution to server 20,in this example.

[0031] As evident from FIG. 1a and the foregoing description, thisexample illustrates a unidirectional, or simplex, communicationsapproach, for ease of this description. It will be appreciated by thoseskilled in the art that bi-directional, or duplex, communications may becarried out by providing another transmitter-receiver pair forcommunicating signals in the opposite direction (router 18 to computer2).

[0032] The communications arrangement of FIG. 1a may be utilized inconnection with a wide range of applications, beyond the simplecomputer-to-network example suggested by FIG. 1a. For example, it iscontemplated that each of multiple computers in an office or otherworkspace may communicate with one another and with a larger network byway of modulated light to a central receiver within the room, and alsobetween rooms by way of relayed communications along hallways or in aspace frame. Other indoor applications for this optical wirelesscommunications may include the communication of video signals from acomputer or DVD player to a large-screen projector. It is furthercontemplated that optical wireless communications in this fashion may becarried out in this manner but on a larger scale, for example between oramong buildings.

[0033] The positioning of micromirror assembly 10 must be preciselycontrolled to aim the modulated laser beam at receiver 17, and thusoptimize the signal-to-noise ratio of the transmitted signals. It iscontemplated that this precision positioning is preferably accomplishedby way of calibration and feedback, so that the mirror is able to senseits position and make corrections. Previous efforts toward providingsuch positioning, in connection with the present invention, haveincluded external sensors such as illustrated in FIG. 1a.

[0034] As shown in this example, the reflected laser beam impinges beamsplitter 12. Beam splitter 12 transmits the majority of the energy toreceiver 17, but reflects a portion of the energy to position sensitivedetector (PSD) 15. PSD 15 provides signals to control circuitry 14,indicating the position of the reflected light that it receives. Controlcircuitry 14 then issues control signals to micromirror assembly 10 todirect its angle of reflection in response to the signals from PSD 15,optimizing the aim of the directed laser beam at receiver 17. In oneexample, during setup of the transmission, micromirror assembly 10 andPSD 15 “sweeps” the aim of the directed laser beam across the generalarea of receiver 17. In response, receiver 17 issues signals to controlcircuitry 14 over a secondary communications channel (not shown),indicating the received energy over time. These “pings” may be comparedwith the instantaneous position of micromirror assembly 10 as measuredby PSD 15, to calibrate and optimize the aim of micromirror assembly 10to achieve maximum energy transmission. Once this aim is set,communications may then be carried out. It is contemplated, however,that adjustments may be necessary due to external factors such asbuilding or equipment movement and the like. These adjustments may becarried out by way of feedback from receiver 17 (either over thesecondary channel or as transmit mode feedback in a duplex arrangement),or by periodically repeating the measurement and sweeping.

[0035] The provision of beam splitter 12 and PSD 15 in transmitteroptical module 5 as shown in FIG. 1a provides the desired feedbackcontrol of the reflection of the laser beam. However, from a cost andreliability standpoint, it is desired to reduce the number of componentsin the transmitter optical module. Referring now to FIG. 1b, acommunications system according to the preferred embodiments of theinvention, in which the packaged micromirror assembly includes integralposition sensing capability, will now be described.

[0036] As shown in FIG. 1b, transmitter optical module 25 includespackaged micromirror assembly 21 that directly reflects the laser beamfrom laser 6 to receiver 17, without a beam splitter or other externalcomponents interposed in the path of the beam. Packaged micromirrorassembly 21, as will be described in detail below, includes sensingcapability by way of which the orientation of the mirror is detected anda signal generated that is applied to control circuit 24. In response,control circuit 24 provides electrical signals to packaged micromirrorassembly 21 to position the mirror, so that the beam may impingereceiver 17 in an optimal manner.

[0037] Because of the in-package positional feedback provided bypackaged micromirror assembly 21, transmitter optical module 25 may bemanufactured at significantly lower cost. In addition, by eliminatingthe beam splitter, transmitter optical module 25 avoids the inherentloss of beam intensity that is otherwise directed to the positionsensitive detector.

[0038] Referring now to FIGS. 2a and 2 b, packaged micromirror assembly21 according to a first preferred embodiment of the invention will nowbe described. As shown in FIGS. 2a and 2 b and as will be described infurther detail below, mirror element 41 is formed of a single piece ofmaterial, preferably single-crystal silicon, photolithographicallyetched in the desired pattern, to form mirror surface 29 and itssupporting hinges and frame. To improve the reflectivity of mirrorsurface 29, mirror element 41 is preferably plated with a metal, such asgold or aluminum. In its assembled form, as shown in FIGS. 2a and 2 b,four permanent magnets 53 are attached to mirror element 41, at a 90°relative orientation from one another, to provide the appropriaterotation. Magnets 53 may be formed of any permanently magnetizablematerial, a preferred example of which is neodymium-iron-boron.

[0039]FIGS. 3 and 3a through 3 d illustrate mirror element 41 in furtherdetail. Mirror element 41 includes a frame portion, an intermediategimbals portion, and an inner mirror portion, all preferably formed fromone piece of crystal material such as silicon. In its fabrication,silicon is etched to provide outer frame portion 43 forming an openingin which intermediate annular gimbals portion 45 is attached at opposinghinge locations 55 along first axis 31. Inner, centrally disposed mirrorportion 47, having a mirror 29 centrally located thereon, is attached togimbals portion 45 at hinge portions 55 on a second axis 35, 90 degreesfrom the first axis. Mirror 29, which is on the order of 100 microns inthickness, is suitably polished on its upper surface to provide aspecular surface. Preferably, this polished surface is plated with ametal, such as aluminum or gold, to provide further reflectivity. Inorder to provide necessary flatness, the mirror is formed with a radiusof curvature greater than approximately 2 meters, with increasingoptical path lengths requiring increasing radius of curvature. Theradius of curvature can be controlled by known stress control techniquessuch as, by polishing on both opposite faces and deposition techniquesfor stress controlled thin films. If desired, a coating of suitablematerial can be placed on the mirror portion to enhance its reflectivityfor specific radiation wavelengths.

[0040] Mirror element 41 includes a first pair of permanent magnets 53mounted on gimbals portion 45 along the second axis, and a second pairof permanent magnets 53 mounted on extensions 51, which extend outwardlyfrom mirror portion 47 along the first axis. In order to symmetricallydistribute mass about the two axes of rotation to thereby minimizeoscillation under shock and vibration, each permanent magnet 53preferably comprises a set of an upper magnet 53 a mounted on the topsurface of the mirror element 41 using conventional attachmenttechniques such as indium bonding, and an aligned lower magnet 53 bsimilarly attached to the lower surface of the mirror assembly as shownin FIGS. 3a through 3 d. The magnets of each set are arranged seriallysuch as the north/south pole arrangement indicated in FIG. 3c. There areseveral possible arrangements of the four sets of magnets which may beused, such as all like poles up, or two sets of like poles up, two setsof like poles down; or three sets of like poles up, one set of like poledown, depending upon magnetic characteristics desired.

[0041] By mounting gimbals portion 45 to frame portion 43 by means ofhinges 55, motion of the gimbals portion 45 about the first axis 31 isprovided and by mounting mirror portion 47 to gimbals portion 45 viahinges 55, motion of the mirror portion relative to the gimbals portionis obtained about the second axis 35, thereby allowing independent,selected movement of the mirror portion 47 along two different axes.

[0042] The middle or neutral position of mirror element 41 is shown inFIG. 3a, which is a section taken through the assembly along line A-A ofFIG. 3. Rotation of mirror portion 47 about axis 35 independent ofgimbals portion 45 and/or frame portion 43 is shown in FIG. 3b asindicated by the arrow. FIG. 3c shows the middle position of the mirrorelement 41, similar to that shown in FIG. 3a, but taken along line B-Bof FIG. 3. Rotation off the gimbals portion 45 and mirror portion 47about axis 31 independent of frame portion 43 is shown in FIG. 3d asindicated by the arrow. The above independent rotation of mirror 29 ofmirror portion 47 about the two axes allows direction of optical beam 13as needed by the optical switch units.

[0043] In order to protect hinges 55 from in-plane shock during handlingand shipping, stops 57 may be provided, as described in theabove-incorporated application Ser. No. 09/310,284. According to anotheroptional feature of the invention, lock down tabs associated with eachhinge are provided, also as described in the above-incorporatedapplication Ser. No. 09/310,284.

[0044] Referring back to FIG. 3, extensions 51 are preferably providedwith laterally extending tabs 51 a, which can be used to clamp down themirror portion during assembly to thereby provide additional stressprotection.

[0045] Mirror element 41, in this embodiment of the invention, restsupon and is attached to shelf 34 of body 30. Shelf 34 lies inwardly ofwindow shelf 32, upon which transparent window 31 rests and is attached.Window 31 may be formed of conventional microscope slide glass, or of atransparent plastic such as LEXAN plastic. It is highly preferred thatthe dimensions and locations of shelves 32, 34, as well as the bottomwell of body 30, be selected so that the maximum deflection of mirror 29is stopped by one of magnets 53 impacting body 30 without mirror 29itself impacting the inner surface of window 31. Additionally, it ispreferred that the maximum deflection of mirror 29 is limited, by body30, to an angle that is well below that which overstresses hinges 55.

[0046] Further detail regarding the construction and method ofmanufacturing packaged micromirror assembly 21 according to thepreferred embodiments of the invention, including alternative methodsfor such manufacture, is provided in copending provisional applicationNo. 60/234,074, filed Sep. 20, 2000, entitled “Molded Packages forOptical Wireless Network Micromirror Assemblies”, commonly assignedherewith and incorporated herein by this reference.

[0047] As shown in the cross-section of FIG. 2b, packaged micromirrorassembly 21 includes position sensor 63 physically disposed betweenmirror assembly 41 and driver coils 36, and thus in close proximity tomirror element 41. Sensor 63 is preferably mounted to body 30 prior tothe attachment of mirror element 41, as sensor 63 is positioned betweenbody 30 and mirror element 41. Position sensor 63 is electricallyconnected to leads 61, to provide electrical signals (or response, inthe passive sense) to external circuitry such as control circuitry 24 intransmitter optical module 25. In this example, therefore, packagedmicromirror assembly 21 provides position sensing signals to controlcircuitry 24 on leads 61, and receives position input signals on leads39. The complete feedback sensing and control response is thus providedwithin packaged micromirror assembly 21 itself, according to the presentinvention.

[0048] According to a first preferred embodiment of the invention, asshown in FIGS. 4a and 4 b, the mechanism by way of which the position ofmirror 29 is sensed uses incident light produced below the surface ofmirror 29 and reflected from its underside. As shown in FIG. 4a,position sensor 63 according to this first embodiment of the inventionis a printed circuit board having light-emitting-diode (LED) 68 thatemits light through point aperture 66 toward the underside of mirror 29.As shown in FIG. 4b, this arrangement of LED 68 and aperture 66 providesdistribution 71 of light intensity that is substantially Gaussian inshape, with the light intensity imparted to mirror 29 being at a maximumat its center point, and falling off sharply away from the center. Forexample, a standard deviation of on the order of 40° for distribution 71is contemplated to be suitable for use in connection with thisembodiment of the invention. This distribution 71 of light intensity isused to determine the position of mirror 29, as will be described below.

[0049] Sensor 63 also includes four light detectors 65, spaced 90° fromone another as shown in FIG. 4a. In this example, detectors 65 x+, 65 x−are located along the positive and negative horizontal axes, usingaperture 66 as the origin; detectors 65 y+, 65 y− are located along thepositive and negative vertical axes in similar fashion. It is preferredthat detectors 65 are placed at the same radial distance from aperture66. Detectors 65 are preferably electrically coupled or connected toexternal circuitry, for example via leads 61 (FIG. 2b).

[0050] In operation, sensor 63 is able to detect changes in theorientation of mirror 29 from variations in the light intensity sensedby detectors 65, as will now be described relative to FIG. 4b. Theexample of FIG. 4b illustrates the operation of sensor 63 for rotationin one axis only, for clarity of description; it will of course beunderstood by those skilled in the art, from this example, that theoperation of sensor 63 in two axes will be similar. In any rotation, theintensity of the light emitted by LED 68 through aperture 66 will beapplied to the underside of mirror 29 in a manner with the point ofhighest intensity at the center of mirror 29. However, the location ofmirror 29 from which light reflects to each of detectors 65 and, givendistribution 71 of this light, the intensity of the light reflected todetectors 65, varies with the rotational orientation of mirror 29. Inthe null, or flat, position N of mirror 29, as shown in FIG. 4b, thelight that will be reflected by mirror 29 to each of sensors 65originates from aperture 66 at substantially the same angle relative tothe normal (i.e., perpendicular to the surface of LED 68), as shown bypaths 73 ₀+ and 73 ₀− to sensors 65 x+, 65 x−, respectively. From thisposition of mirror 29, equal light intensity will be sensed by detectors65 x+, 65 x−.

[0051] Upon the rotation of mirror 29 into a rotated position 29′, asshown in FIG. 4b, detectors 65 x+, 65 x− will sense different magnitudesof light intensity. This differential magnitude is due to the change inthe paths traveled by the emitted light. As shown in this example, withmirror 29 rotated toward detector 65 x−, path 73′− traveled by lightreflected to detector 65 x− originates from aperture 66 at an anglefarther from normal than when in the null position. As a result,detector 65 x− will receive lower intensity reflected light from mirror29 in rotated position 29′. On the other hand, path 73′+ traveled bylight reflected to detector 65 x+ with mirror 29 in position 29′originates from aperture 66 at an angle closer to normal than in thenull position. Because of the significantly higher intensity of lightimparted by LED 68 through aperture 66 at points nearer the center ofmirror 29, detector 65 x+ will receive a higher magnitude of light withmirror 29 in rotated position 29′ than from mirror 29 in its nullposition.

[0052] As a result of the variations of detected reflected light withthe rotational position of mirror 29, as sensed by detectors 65, sensor63 can generate or modulate electrical signals indicative of theintensity of detected light. These signals can then be used to determinethe rotational position of mirror 29, and thus to control thepositioning of mirror 29 to aim the laser beam toward the desiredreceiver.

[0053] In the foregoing implementation of the first preferred embodimentof the invention, a single light source is defined by aperture 66, withmultiple detectors 65 angularly arranged at a common radius from thecenter axis. Alternatively, multiple light sources may be angularlyarranged away from the center axis, for example at the locations ofdetectors 65 illustrated in FIG. 4a, in combination with a singledetector located at the center axis (i.e., at the location of aperture66 in FIG. 4a). According to this alternative, the multiple lightsources (e.g., LEDs and apertures) would illuminate the underside ofmirror 29 in a pattern from which the path intensities could be derived.For example, the multiple LEDs could be activated in a temporalsequence, with the detected reflected light analyzed according to asynchronized sequence in order to determine the relative lightintensities along each path. The multiple light sources could emit theirlight simultaneously, but at different modulation frequencies, in whichcase signals corresponding to the detected light would be demodulated todetermine a frequency spectrum indicative of the relative pathintensities.

[0054] In any case, additional intelligence may be provided withinsensor 63, if desired, to facilitate the feedback and control of mirror29. Referring back go FIG. 2b, memory 77 is provided on the printedcircuit board of sensor 63, for storing calibration information. Becauseof manufacturing tolerances, it is contemplated that a flat, null,position of mirror 29 may not correspond to a balanced light intensityreading among detectors 65; as a result, the intensity readings mayrequire calibration, from assembly to assembly, to ensure that a “zero”electrical signal corresponds to a flat mirror orientation, even if thedetected light intensities are not balanced. Memory 77 is thereforeoptionally provided to store calibration data for each of detectors 65,or for the detectors 65 in the aggregate, so that the resultingelectrical signal presented by assembly 21 corresponds to the deviationof mirror 29 from null. In this regard, memory 77 is preferably anon-volatile read/write memory, such as an EEPROM. For example, themanufacturer may pre-calibrate each assembly 21 in factory testing, andstore the calibration values in memory 77. The users of assemblies 21can then rely on the electrical signals to indicate mirror orientation,without performing additional calibration at the system application.

[0055] Referring now to FIGS. 5a through 5 c, packaged micromirrorassembly 21′ according to a second preferred embodiment of the inventionwill now be described in detail. The components of packaged micromirrorassembly 21′ according to this embodiment of the invention are, for themost part, similar to those described above in packaged micromirrorassembly 21. By way of example, the body of packaged micromirrorassembly 21′ is formed by a transfer molded approach, as described inthe above-incorporated provisional application No. 60/234,074; ofcourse, other packaging techniques may also be used in connection withthe present invention. According to this preferred embodiment of theinvention, however, packaged micromirror assembly 21′ includescapacitive sensor 80, for detecting the rotational position of mirror 29by variations in capacitance.

[0056] As shown in FIG. 5a, capacitive sensor 80 has a conical uppershape, and is disposed between driver coils 36 and mirror element 41.The vertex of capacitive sensor 80 is disposed under the center point ofmirror 29, so that this center point, relative to which the potentialrotations of mirror 29 are made, remains in a fixed position relative tothis vertex, with a small space between sensor 80 and mirror 29 at thispoint.

[0057]FIG. 5b illustrates capacitive sensor 80 in plan view. As shown inFIG. 5b, sensor 80 is segmented into multiple sections that areelectrically isolated from one another. In this example, sensor 80 hasfour segments, each corresponding to a quadrant of the plane defined bythe two axes of rotation of mirror 29. In this example, each of magnets53 are centered within one of the segments of sensor 80 (rather thanbetween segments).

[0058] As a result of this construction of sensor 80, rotations ofmirror 29 from a null position will place mirror 29 closer to one ormore of the sensor segments than others. In the example shown in FIG.5c, mirror 29 is rotated into rotated position 29′, in which case mirror29 is nearer the right-hand segment of sensor 80 (as shown in FIG. 5c)than to the left-hand segment.

[0059] The variation in the distance between mirror 29 and sensor 80 maybe converted into an electrical signal by considering mirror 29 as oneplate of a capacitor, and each of the segments of sensor 80 as opposingplates of multiple capacitors. The distance between mirror 29 and eachsegment of sensor 80 will determine the value of capacitance betweenthese two plates. As is fundamental in the art, capacitance is inverselyproportional to the dielectric distance. This capacitance value is thenmeasured by conventional techniques, for example by the application of ahigh frequency input signal between mirror 29, on one hand, and each ofthe segments of sensor 80, on the other hand; the response of thecapacitors to the high frequency input signal will indicate the value ofcapacitance between each segment of sensor 80 and mirror 29.Alternatively, the capacitors established by the various segments ofsensor 80 may be arranged into a conventional capacitance bridge, by wayof which the various capacitance legs may be determined in the knownmanner. The resulting measurements may be communicated from packagedmicromirror assembly 21′ by way of external leads (e.g., leads 61 ofFIG. 2b).

[0060] Additionally, a memory device may optionally be provided withinpackaged micromirror assembly 21′, for storing calibration values in themanner discussed above relative to assembly 21.

[0061] Alternatively, sensor 80 may be flat, rather than conical. Thisconstruction would provide a lower cost sensor, but would likely resultin reduced sensitivity because of the reduction in capacitance betweenthe flat sensor and mirror 29.

[0062] Further in the alternative, it is contemplated that relativeinductance between sensor 80 and mirror 29 may be detected and used tomeasure the relative orientation of mirror 29.

[0063] Similarly as described above relative to the first embodiment ofthe invention, the capacitance measurement approach of packagedmicromirror assembly 21′ provides direct feedback of the position ofmirror 29, without requiring external components such as a beam splitterand a position sensitive detector as shown in FIG. 1a. This provides anoptical transmitter module that can be fabricated at lower cost, withhigher reliability. Additionally, the full intensity of the directedlaser beam may be used for data transmission, without the lossesinherent in the use of a beam splitter.

[0064] While the present invention has been described according to itspreferred embodiments, it is of course contemplated that modificationsof, and alternatives to, these embodiments, such modifications andalternatives obtaining the advantages and benefits of this invention,will be apparent to those of ordinary skill in the art having referenceto this specification and its drawings. It is contemplated that suchmodifications and alternatives are within the scope of this invention assubsequently claimed herein.

We claim:
 1. A packaged micromirror assembly, comprising: a mirrorelement; a plurality of driver elements responsive to electrical signalelements for orientating the mirror element; a body encasing at leastone driver element and to which the mirror element is attached; and asensor, disposed beneath the mirror element, for detecting theorientation of the mirror.
 2. The assembly of claim 1, wherein thesensor has electrical leads extending from the body for presenting anindication of the orientation of the mirror.
 3. The assembly of claim 2,further comprising: a memory for storing calibration values of thesensor.
 4. The assembly of claim 1, wherein the sensor comprises: atleast one light source for illuminating an underside of the mirrorsurface; and at least one detector for detecting light imparted by theat least one light source and reflected from the underside of the mirrorsurface; wherein the combination of the at least one light source and atleast one detector provide a plurality of reflection paths over whichthe intensity of reflected light is measured.
 5. The assembly of claim1, wherein the sensor comprises: a light source for illuminating anunderside of the mirror surface; and a plurality of detectors, angularlyarranged under the mirror surface, for detecting the intensity of lightfrom the light source after reflection from the underside of the mirrorsurface.
 6. The assembly of claim 5, wherein the light source comprises:a light-emitting diode; and an aperture directed at a center point ofthe underside of the mirror surface, through which light from thelight-emitting diode passes.
 7. The assembly of claim 1, wherein thesensor comprises: a plurality of light sources, angularly arranged underthe mirror surface, each for illuminating an underside of the mirrorsurface; and a detector, located coaxially with the mirror surface fordetecting the intensity of light from each of the plurality of lightsources after reflection from the underside of the mirror surface.
 8. Anelectronic system, comprising: a data source, for generating data to becommunicated to a receiver; and a transmitter optical module,comprising: a light source, coupled to the data source, for generating amodulated directed light beam; and a packaged micromirror assembly fordirecting the directed light beam at the receiver, comprising: a mirrorelement formed of a single piece of crystalline material, the mirrorelement having a frame, a mirror surface, and a plurality of hinges; atleast one permanent magnet attached to the mirror element; a pluralityof coil drivers, in proximity to the at least one permanent magnet, fororienting the mirror element; a body encasing the plurality of coildrivers, and to which the mirror element is attached; and a sensor,disposed between the body and the mirror element, for detecting theorientation of the mirror.
 9. The system of claim 8, wherein the datasource comprises a computer.
 10. The system of claim 8, wherein thelight source comprises a laser.
 11. The system of claim 8, wherein thepackaged micromirror assembly further comprises: control circuitry,coupled to the sensor and to the driver coils, for applying a signal tothe driver coils responsive to the detected orientation of the mirror.12. The system of claim 11, wherein the sensor has electrical leadsextending from the body to the control circuitry, for presenting anindication of the orientation of the mirror.
 13. The system of claim 8,further comprising: a memory for storing calibration values of thesensor.
 14. The system of claim 8, wherein the sensor comprises: atleast one light source for illuminating an underside of the mirrorsurface; and at least one detector for detecting light imparted by theat least one light source and reflected from the underside of the mirrorsurface; wherein the combination of the at least one light source and atleast one detector provide a plurality of reflection paths over whichthe intensity of reflected light is measured.
 15. The system of claim 8,wherein the sensor comprises: a light source for illuminating anunderside of the mirror surface; and a plurality of detectors, angularlyarranged under the mirror surface, for detecting the intensity of lightfrom the light source after reflection from the underside of the mirrorsurface.
 16. The system of claim 15, wherein the light source comprises:a light-emitting diode; and an aperture directed at a center point ofthe underside of the mirror surface, through which light from thelight-emitting diode passes.
 17. The system of claim 8, wherein thesensor comprises: a plurality of light sources, angularly arranged underthe mirror surface, each for illuminating an underside of the mirrorsurface; and a detector, located coaxially with the mirror surface fordetecting the intensity of light from each of the plurality of lightsources after reflection from the underside of the mirror surface.
 18. Amethod of transmitting data signals, comprising: generating a modulatedlight beam; orienting a micromirror to reflect the modulated light beamfrom an upper surface of the micromirror to a receiver; directing lightat an underside of the micromirror; detecting light reflected from theunderside of the micromirror at a plurality of locations arranged at aplurality of angles; and determining the orientation of the micromirrorfrom the detected reflected light at the plurality of locations.
 19. Themethod of claim 18, wherein the orienting step comprises: selectivelyenergizing a plurality of coil drivers, each in proximity to at leastone permanent magnet attached to the underside of the micromirror. 20.The method of claim 19, wherein the orienting step orients themicromirror to a null position; and further comprising: detecting therelative light intensity at each of the plurality of locations with themicromirror at the null position; and storing, in a memory, calibrationvalues corresponding to the micromirror at the null position.